For most of the Second World War, scientists and administrators
of the Manhattan Project firmly believed that they were in a race with
Germany to develop the atomic bomb. As it turns out, the German
atomic program did not come close to developing a useable weapon.
Allied planners were only able to confirm this, however, through the ALSOS
intelligence mission to Europe toward the end of the war. Atomic research
was also conducted in Japan, but as was suspected by the Allies, it did not
get very far.

Fission, the basic
process that makes nuclear weapons possible, was first discovered in Berlin in
December 1938. Though the beginning of the war was still ten
months away, when news of
the German discovery arrived in the United States, it caused a
considerable amount of alarm. Not only did it now appear for the
first time that an "atomic bomb" was possible, but it was Nazi
Germany that seemed to be ahead in this new and potentially worst-of-all
arms races. Many of the scientists that took a leading role in
alerting the United States government to this danger, such as Albert
Einstein, Enrico Fermi, and Leo Szilard, were
recent émigrés from Europe who felt the threat from Nazi Germany especially
acutely. Further, German science and industry appeared to be capable
of the kind of massive development program that building an atomic bomb
would require. During the war, for example, Germany had become the
first nation in the world to develop and use jet fighters (Me-262s), cruise
missiles (V-1s), and ballistic missiles (V-2s). Although we now know
that the United States and Britain won the race for the bomb, it is
important to remember that this outcome was by no means certain, let alone
obvious, during the early years of the war.

The
German atomic weapons program began with a secret April 1939 conference in
Berlin, which resulted in the Ministry of Education initiating a formal uranium
research program and banning the export of uranium to other nations.
That same month, Paul Harteck (right), a German
chemist, wrote the War Office to alert it to the danger of "an
explosive many orders of magnitude more powerful than the conventional
ones" that would give "that country which first makes use of it
an unsurpassable advantage." Hans Geiger (of "Geiger counter"
fame) confirmed that this was a very real possibility, and the War Office
threw its support behind uranium research. The "German Manhattan
Project" had begun, five months before President
Franklin D. Roosevelt would read Einstein's letter
warning of the potential for nuclear weapons.

The
most destructive war in human history began with the German invasion of
Poland on September 1, 1939. That same month Kurt Diebner
(left), the head of the War Office's fission research, summoned Geiger,
Otto Hahn (below left), and other physicists to Berlin to discuss the
feasibility of nuclear weapons. By the end of a second meeting that
month (to which Werner Heisenberg had been invited as well), the German
scientists had agreed to begin research into pile
design, isotope
separation, fast-neutron fission, and other critical aspects of an
atomic weapons program. German uranium research continued and, in
1940, it began to benefit from the successes of the Nazi armies that were
overrunning Western Europe. In Belgium, Germany captured an ample supply of
uranium; in France, Germany captured Frédéric
Joliot and his cyclotron;
in Norway, Germany captured a Norsk Hydro Plant
that was the world's largest producer of heavy water; and in Denmark,
Germany captured Niels Bohr. (The American
embassy had offered Bohr safe passage to the United States during the
invasion, but Bohr chose to stay behind and help organize the peaceful
resistance to the Nazi occupation.) By October 1940, Heisenberg was
conducting at the Kaiser-Wilhelm Institute a series of pile experiments
that were comparable to those being carried out that same year by Fermi at Columbia University.
The race still appeared to be neck-and-neck.

Although
there was no way for the Americans to know it at the time, scientists in
the United States began in around 1941 to pull far ahead of their
counterparts in Germany. In January of that year, a physicist by the
name of Walter Bothe made a critical miscalculation that caused Germany to
mistakenly rule out graphite as a possible moderator. (Szilard had recently
succeeded in convincing scientists in the still-neutral United States to
keep secret the results of their atomic research, and, as a result, the
Germans could not learn of their mistake from the open scientific
literature.) This left expensive heavy water as the only viable
moderator for a pile, and the
plutonium path to the bomb was only possible if a chain-reacting
pile could first be made to work. As for the uranium path to the
bomb, German researchers concentrated most of their early isotope
separation effort on the inefficient thermal
diffusion method (left). After this was eventually abandoned, they
concluded that the other methods of producing weapons-grade uranium would
only be possible at a very great expense and with no assurance of
success. (They were correct in this. It took years of extremely
expensive work at Oak
Ridge to produce enough uranium-235 for one atomic bomb.)
Thus, by mid-1941, German researchers had become quite pessimistic about
the feasibility of any sort of nuclear weapon.

German atomic research began to languish. The notoriously
inefficient Nazi bureaucracy, as well as possible doubts by German
scientists about the Nazi regime itself, contributed to the ineffectiveness
of German atomic research. In 1941, the German Post Office was also
funding uranium research separately from Heisenberg's work with the War
Office. A physicist by the name of Fritz Houterman
was closely associated with this effort, however, and he withheld as much
information as he could from his German superiors, possibly attempting to
discourage further uranium research in favor of the more complicated
plutonium route. (Houterman, a half-Jewish
Austrian communist, held no love for the Nazis.) After the war, many
other German physicists, including most notably Heisenberg himself, also
claimed to have been secretly not trying very hard in their war
research. Whether this was an attempt after the fact to excuse their
failure and/or justify their work on behalf of the Nazi regime is still a
subject of intense debate among historians today.

An
incident in September 1941 helps to illustrate the confused and ambiguous
nature of possible resistance by German scientists to the German atomic
bomb project. Heisenberg, who by this time was the leader of the
German effort, asked for a meeting with his old friend and mentor
Bohr. According to Heisenberg, he was there to ask Bohr's opinion of
the morality of work on the atomic bomb. For his part, Bohr wanted no
part of German atomic research and was careful to say nothing of
importance. Heisenberg did tell Bohr of Germany's atomic research and
even passed to Bohr a diagram of the German pile in Berlin, but whether he
did so in order to warn Bohr, and hence the Allies, or only to get Bohr's
advice (or even mislead him), it is impossible to know. In 1943, the
Danish underground helped Bohr to escape to Britain (via neutral
Sweden). He got away only days before he was to be arrested by the
Gestapo, and he brought with him the drawing of Heisenberg's pile.

Comparatively little progress was made toward a German atomic bomb from
about 1942 onwards. Many German scientists, including Heisenberg,
continued to make pleas for greater government funding, but as the war
turned against Germany, it increasingly focused its science and industry on
more immediate war needs. German pile work continued to focus until
the end on heavy water piles, and this work was hampered by a series of
attacks that were made on the Norsk Hydro heavy
water plant by American aircraft, British commandos, and the Norwegian
resistance. In the final year of the war, aerial bombing and
eventually the advance of Allied ground troops also disrupted their
research. When Germany surrendered in May 1945, its atomic
researchers were still struggling to reach critical mass
with a pile, a goal Fermi
had first achieved at the Met Lab in December
1942.

For most of the war, however,
the success or failure of the German atomic program remained unknown to the
Allies who knew little about what progress, if any, had been made. They
knew that Germany had gathered sufficient quantities of uranium to do
research and that it was very interested in the Norwegian heavy water, but
beyond that there were only rumors. When Bohr told scientists at Los Alamos of his
strange conversation with Heisenberg, no one was certain quite what to make
of the unusual German pile design. At that point, they knew for
certain that Germany was pursuing nuclear weapons but little else was
clear. After Allied troops landed in France on June 6, 1944
("D-Day," right), it finally became possible to physically search
Europe for signs of German atomic research. This was accomplished by
the "ALSOS Mission."

The ALSOS team was led by Lt. Colonel Boris T. Pash, an Army intelligence officer who had earlier
taken part in the security investigation of Robert
Oppenheimer. Because the members of the ALSOS team would at
times be going into "no man's land" -- or even behind enemy lines
-- in search of information, they were not told any details of the
Manhattan Project. This way, if they were captured, they could reveal
nothing of use to the Germans. The mission began in Italy and followed
closely behind the Allied armies as they pushed deeper into Europe and,
ultimately, into Germany itself. Although proving a negative is
always difficult, after months of investigation the ALSOS team found no
indications of massive German nuclear production facilities of the sort
that had been built at Hanford
or Oak Ridge. In late November 1944, ALSOS representatives
uncovered strong evidence at the University of Strasbourg that the German
program had not gotten beyond the research and development stage, but it
was not until April 1945, only weeks before the final German surrender,
that the bulk of the German uranium was captured and any final fears of a
Nazi bomb were alleviated. After the war, ten of the top German
atomic researchers were interned in a British intelligence "safe
house" in Farm Hall, Great Britain (above left), for six months.
All of their conversations were secretly recorded. The significance
of what they said to each other is still a matter of debate, but the
transcripts of their discussions do make it clear just how far away from a
useable weapon the German atomic program remained at war's end.

With the surrender of Germany, only Japan remained as
a possible atomic threat. Japanese physicists had noted the discovery
of fission before the war, and they did inform the Japanese Army of the
danger. Some research was conducted at a Tokyo laboratory into
various methods of uranium enrichment, but comparatively little progress was
made. In early 1943, a group of Japanese experts concluded that,
while it was true that the United States was probably trying to build an
atomic bomb, it might take Japan ten years or more to build one.
Accordingly, little further research into nuclear energy was conducted in
Japan beyond the construction of one cyclotron in Kyoto.

The text for this page is original to the
Department of Energy's Office
of History and Heritage Resources. "Atomic" and
"nuclear" are basically synonymous; much as the term
"pile" gradually gave way to "reactor,"
"atomic" was gradually replaced by "nuclear" during the
later years of the Manhattan Project and afterwards. For the German
atomic program, see David Irving, The German Atomic Bomb (New York:
Simon and Schuster, 1968). On the ALSOS mission, see Vincent C.
Jones, Manhattan: The Army and the Atomic Bomb, United
States Army in World War II (Washington: Center of Military History, United
States Army, 1988), 280-291. For the Japanese program, see Pacific
War Research Society, The Day Man Lost (Kodansha International,
1972), and Deborah Shapley, "Nuclear Weapons History: Japan's Wartime
Bomb Projects Revealed," Science 199 (1978), 152. It
should be noted also that two authors have in recent years argued Japan and
Germany were much closer than has been generally realized to developing
nuclear weapons. In Japan's Secret War: Japan's Race Against Time
to Build Its Own Atomic Bomb (New York: Marlowe & Company, 1995),
Robert K. Wilcox argues that Japan came extremely close to
completing a bomb. In The Nuclear Axis: Germany, Japan and the
Atom Bomb Race, 1939-1945 (Phoenix Mill, UK: Sutton Publishing Limited,
2000), Philip Henshall implies that both Germany
and Japan made much more progress than is generally known and that this may
have been covered up by the Allies for some reason that relates somehow to
the Cold War. Neither author provides footnotes, however, and it is
therefore often impossible to determine what their source is for any
particular statement. Further, their most important (and
controversial) arguments often rely more on supposition and the raising of
"unanswered questions" than on detailed, verifiable
evidence. Their arguments have not been generally accepted within the
historical profession. Still, there is interesting information in
both regarding their subjects, and -- used with caution -- they can be
useful sources of information. The photograph of the V-2 rocket being
tested in Florida after the war is courtesy the National Oceanic and Atmospheric Administration's
photo library. The
photograph of Werner Heisenberg with Niels Bohr
is courtesy the Fermi National Accelerator
Laboratory. The diagram illustrating the liquid thermal
diffusion method is reproduced from the Department
of Energy report Linking
Legacies: Connecting the Cold War Nuclear Weapons Production Processes to
their Environmental Consequences (Washington: Center for Environmental
Management Information, Department of Energy, January 1997), 138.
The photograph of "D-Day" is courtesy the National Archives (NARA). All
other photographs are courtesy NARA and are reprinted in Jeremy Bernstein,
ed., Hitler's Uranium Club: The Secret Recordings at Farm Hall
(Woodbury, NY: American Institute of Physics, 1996).